tonight, the night ambassador chris stevens and others were killed. jonathan karl tells us what state department officials are revealing. >> reporter: ahead of a major congressional hearing into what happened on that attack on our consulate in libya. we are hearing new details, details that we have never heard before, about what went, what went down. this is significantly different than what we were told at the time. at the time, as you recall, we were told it was a protest that went bad. and became an attack. now we are told, there was no protest going on outside that embassy. the first indication that they heard anything outside the walls of the embassy of the consulate compound was an explosion and gunfire, gunfire. they looked through a camera to see what was going on. and we are told they saw a large number of armed men coming and approaching the compound. we are told it was a very complex attack. without precedent in u.s. diplomatic history. never seen an attack like this in libya or anywhere else. we were told, by this, this senior state depart